Below ground chemical and microbial community responses of wood ash addition to a hardwood forest in central Ontario

Abstract

The use of wood ash as a soil amendment remains restricted in many parts of Canada. To better understand belowground biogeochemical responses to wood ash, soil solution chemistry was measured over 3 years following the application of wood ash (0, 2.5, 5.0, and 7.5 Mg·ha−1) at a hardwood stand in Ontario, after which soil microbial response was assessed using 16S rRNA gene and internal transcribed spacer sequencing. Metal concentrations in the locally sourced wood ash were below provincial regulatory limits. Significant increases in soil solution pH were observed within the forest floor in the first year of the trial, and significant increases in calcium and magnesium were also observed in later years of the trial. Concentrations of most metals in soil water either decreased or exhibited no significant change in response to wood ash. There was an increase in diversity and richness of soil prokaryotic groups in the FH horizon at the highest wood ash treatment that is most likely linked to the large increase in pH. This study indicates that wood ash has a strong ameliorative effect on soil and soil water chemistry without major changes to soil microbial communities and is a viable amendment to forest soils at dosages below 5 Mg·ha−1.